"S 





Hollingjer 

pH 83 

MiU Run F03-2193 



AN 



d:XPERIMENTAL RESEARCH 



INCREASE THE PROTECTION OF 



SAFES 



Fire, Dampness, Rust and Fhost 



BY 

E. ISr. HORSFORD, 

LATE RUMFORD PROFESSOE IN HARVARD UNIVERSITY, 



BOSTON: 

ALFRED MUDQE & SON, PRINTERS, 34 SCHOOL STREET. 
1863. 



J 






Entered according to Act of Congress, in the y^ear 1863, by E. N. Horsford, 
in the Clerk's Office of the District Court of the District of Mass. 



SAFES 

FOR 

BOOKS ^ND P^^PERS. 



What are the requisites of a safe for the preservation of 
valuable books and papers ? 

It should be proof against ordinary attempts to break 
open. 

It should provide the largest practicable measure of pro- 
tection against fire. 

It should protect its contents against dampness. 

It should be proof against injury by frost. 

It should be proof against rust. 

It should be as cheap and light as the foregoing requisi- 
tions will permit. 

The experience of the last few years, has practically dem- 
onstrated, what might have been foreseen, that protection 
against fire, can he relative only, not absolute. 

Fire proof buildings, so called, yield when stored with 
combustible materials and for a long time surrounded by 
flame. The best of fire-proof safes are destroyed, when 
exposed to heat sufficiently intense and prolonged. 

This being admitted, how shall the largest practical 
measure of protection against fire be secured ? 

First. By placing the books, papers, etc., to be preserved, 
in an incombustible enclosure, as of iron. 

Second. By surrounding the books, etc., by a non-conduc- 
tor of heat. 



4 



Third, But chiefly by interposing between the incombustible 
enclosure or outer iron shell and the wooden case containing 
the valuables, a substance which on the approach of fire, is 
converted into vapor, absorbing the heat and carrying it 
away. 

If the second and third be omitted, the contents of the 
safe will be destroyed as soon as the iron enclosure has 
become sufficiently hot to set them on fire. If the third 
only has been omitted, the power of preservation will be 
proportioned to the thickness of the layer of non-conducting 
material ; and this, at the best, is relatively but for a brief 
period. If the second, only, has been omitted, since the 
protection arising from vaporization is due to the absorption 
of heat in converting liquid or solid substances into vapor, 
it will obviously be proportioned to the quantity of sub- 
stance so converted into vapor. A hundred pounds of water 
will absorb twice as much heat in passing ofl" in the form of 
steam, as fifty pounds wdll ; and a safe that contains one 
hundred pounds of water to be evaporated, will preserve its 
contents in safety, through a fire in which a safe containing 
but fifty pounds would be destroyed. 

A safe will then, manifestly, be a better protection against 
fire, in proportion as it unites within an incombustible shell, 
the best non-conductor, luith the largest amount of liquid or 
solid to be converted into vapor, at a temperature not dangerous 
to the contents of the safe. 

HOW ARE THE CONTENTS OF A SAFE TO BE PROTECTED 
AGAIXST DAMPNESS? 

The injuries from this cause are, not infrequently, of the 
most serious character. Valuable papers and books become 



mildewed, and in time quite disintegrated, from the moisture 
which condenses upon them. These injuries arise from the 
evaporation of water from the fire resisting composition, 
through cracks imperfectly closed at the time of manufacture, 
or made subsequently by rusting ; or by passing through the 
pores of the wooden case ; or by freezing the water of the 
composition, by the expansion of which the walls are sepa- 
rated from each other and communication established between 
the filling and the chamber of the safe. 

They may be prevented by so constructing the safe as to 
absolutely prevent any communication of water or vapor be- 
tween the filling of the safe and the books and papers. 

HOW IS THE SAFE TO BE PROTECTED AGAINST I^^JURT 
FROM FREEZING ? 

In a climate like ours, a safe may be exposed occa- 
sionally to temperatures below freezing. Any of the safes 
as at present constructed, cannot contain any considera- 
ble quantity of water above that in chemical combination, 
without the danger of bursting by cold. This opening of 
the seams of the safe, at once exposes the contents of the 
case to the exhalation of moisture from the filling. 

The protection against this kind of injury, manifestly lies 
in such construction of the safe as will provide for the expan- 
sion consequent on freezing, without opening the joints or 
seams of the various parts. 

HOW IS RUSTING TO BE PREVENTED ? 

This is one of the agencies by which communication 
between the fiUingr and the chamber of the safe is effected 



6 



after the lapse of time ; and by which the contents of the 
chamber become damp. 

It may be prevented by consuming the oxygen of the air 
which would otherwise act on the iron. Chemical composi- 
tions are prepared which will, by absorbing the oxygen, per- 
fectly protect the iron from corrosion or rust, even in the 
presence of air and water. 

DIFFERENT KINDS OF SAFES IN TJSE. 

The safes at present in use differ from each other in vari- 
ous respects, but chiefly in the capacity of the composition 
employed, to yield vapor. 

The earlier safes were designed chiefly to protect treasure 
against burglary, and were distinguished for their strength. 
Next came safes having non-conducting walls as protection 
against fire. In 1840, a safe appeared which took advantage 
of the principle of vaporization of Avater as protection against 
fire. The alum safe, upon the same principle, was devised 
in 1843. The gypsum safe, also on the same principle, has 
long been in use. The cement safe, in which hydraulic 
cement is substituted for gypsum, has been many years in use. 

In the English safe of Milner, invented in 1840, the space 
between the iron shell and wooden case is occupied with 
closed tubes containing water, these tubes being imbedded 
in saAv dust. On exposure to fire the tubes burst and the 
water, flowing into the saw dust, is converted into vapor, and 
escapes through the joints of the iron shell. 

In the Alum safe, invented by Messrs. Tann, of England, 
and a modification of which is produced in this country, the 
vapor is derived from the water of crystalization of the alum. 



Twenty per cent, of the weight of the alum is converted into 
vapor at 212^^, and eighteen more at 250*^. The remainder is 
given up only at a heat destructive to the contents of the safe. 

In the ordinary gypsum safes, the surplus water added in 
the mixmg, if it does not remain to do injury by charging the 
case and books with dampness or by freezing, is in process of 
time exhaled until there remains only what has entered into 
chemical combination. This latter amounts to twenty per 
cent. Of this, ten per cent, is given up at 212*^, and half 
of the remainder below 300'^. 

The cement safes, as they are usually prepared, contain, 
after setting, and after time for giving up the surplus water, 
about six per cent, of water. Of this, one per cent, goes 
out at 212°.*- 

As the Alum safes are prepared in this country, the alum 
is mixed with pipe clay, and this mixture with fragments of 
brick, the former to absorb the water as the alum melts and 
to facilitate the vaporization ; the latter to give support and 
prevent the composition from falling when the alum melt&. 
The proportion of alum is about one quarter of the whole. 
This would give of water from the composition, at 212^, only 
five per cent., and at 250^, four and a half per cent, more, or 
only nine and a half in all. If the alum were raised to the 
proportion of one half of the whole mixture it would give up 
but ten per cent, of water at 212^, and nine more at 250°, 
or only nineteen per cent, at temperatures not dangerous to 
the contents of the safe. 

In most fires the exposure is for so brief a period that the 
protection in some of the best safes is adequate ; but there 

* These numbers will doubtless vary somewhat, according to tht 
cement used. 



is tlie constant possibility that the fire may be too powerful 
and too protracted for the composition employed, and the 
protection consequently inadequate. 

CAN THE PROTECTION AGAINST FIRE BE INCREASED ? 

The incombustible inclosure is of wrought iron. Nothing 
could be better. 

What is the best practicable non-conductor ? 

What is the best composition for keeping down heat by 
vaporization ? 

A series of experiments has been made to answer these 
two inquiries. 

In answer to the first question, experiments were made, 
among other materials, with 

Infusorial earth, heated to 220''. 

A mixture of Sal Soda and Gypsum, '* 

A mixture of Glaubers Salt and " " 

Set Cement 

Alum and dry Cement " 

Gypsum with Gelatine '* 

A wrought iron cup, containing about 8 ounces of water, 
was filled with each substance in its turn, and the bulb of a 
thermometer imbedded to the same distance from the bottom 
in all. The vessel and its contents were then subjected to 
the same degree of heat. The conducting power, or the 
facility of heating throughout, was measured by the num- 
ber of degrees swept over by the ascending column of 
mercury in successive minutes. 

The range of heat was from 220^ to 572^ 

Infusorial Earth was heated 27° in one minute. 

Sal Soda and Gypsum taken in equal parts, 14° in one 
minute. 



Glaubers Salt and Gypsum, taken in equal parts, 12^ in 

one minute. 

Cement, set and di'ied, 11° in one minute. 

Potash Alum, 3 oz. ) 5° per minute, from 220° to 300°. 
Dry Cement, 6 oz. / 4° per minute, from 300° to 572°. 

~j 2° per minute, from 

Gypsum, 6 oz. and Water, 6 oz. ! 220° to 300°. 
with 3 per cent of Gelatine, ( 4° per minute, from 

3 300^ to 572°. 

From each, the water due to a temperature of 212°, had, 
as already intimated, been driven out. In the cement, alum, 
and g}YSum, there remained water in combination. The 
infusorial earth proved the best conductor, and would of 
course be the poorest substance for filling a safe. Of all, the 
gypsum and gelatine as prepared for this experiment through- 
out the range in which the contents of the safe are secure 
against fire, namely, below 300°, afi'ords the best protection, 
so far as conduction is concerned. 

It is indeed, difficult to conceive of a substance better 
suited for non-conduction than this mass of set plaster and 
gelatine, after.the surplus water alternating with every particle 
of gypsum, has been diiven out, leaving behind an infinity of 
minute cavities rendering the whole porous and non-conduct- 
ing to the last degree. 

How shall this quality be combined most advantageously 
with the second requisite mentioned above, that of supplying 
matter to be vaporized, thereby carrying the heat away ? 

HOW SHALL NON-CONDUCTION AND VAPORIZATION BE 
BEST UNITED? 

Two sets of experiments were undertaken to determine 
this point. The first on a small scale, the second on a large 



10 



and more practical scale. The first was conducted at the 
same time with the series already detailed, and employing 
the same apparatus. The wrought iron cup was filled with 
each mixture in turn, supported at a constant altitude over a 
flame of uniform height, and the thermometer imbedded to the 
same depth in all. The readings of the thermometer and 
watch, were, as a general thing, every minute. 

The temperature of 220^ has been taken as the limit of the 
escape of water passing off" freely. The results are as follows : 



Gypsum, 6 oz. 



AVater 6 oz. with (23 

three per cent, gelatine, j 

In all 68 



'] 45 minutes from 212" to 220^ 
" 220" to 300°. 



Cement, 


6 oz. \ 42 


" 212" to 220\ 


Water, 


6 oz. ) 4 

In all 46 " 


" 220" to 300\ 


Glaubers salt, 5 oz. ~j 32 " 


" 212" to 220". 


Gypsum, 


5 oz. y 


• 


Water, 


1 oz. J 8 " 
In all 40 " 


" 220" to 300 \ 


Sal Soda, 


Soz.") 33 

5 oz. V 

1 oz. J 5 " 
In all 38 " 


*' 212" to 220". 


Gypsum, 




Water, 


» 220° to 300°. 


Alum, 


3 oz. ( 13 " 


" 212° to 220°. 


Dried Cement, 6 oz.j 11 " 
In all 24 " 


" 220° to 300°. 



11 

A glance at these results will show that the protection 
afforded by vaporization from 212^ to 220"", is pretty nearly 
in the order and ratio of the relative quantities of water 
escaping at or below 212^, in the several compositions here 
employed. 

Gypsum, gelatine and water had 6 oz. water. 
Cement, 6 oz. " 

Glaubers salt and gypsum, 4.2 oz. "• 

Sal Soda and gypsum, 3.87 oz.'' 

Alum, .57 oz. " 

The superiority of the first four of the series, is manifestly 
due solely to the quantity of water they Avere in condition to 
give out. Gypsum and cement, as ordinarily set and dried, 
would have appeared at the bottom of the series. Set gyp- 
sum from which the surplus water has evaporated, contains, 
as already mentioned, but ten per cent of water, that may be 
driven out at 212^. In the p-eparation here employed, , in 
which the gelatine is made to increase the capillary power of 
the gypsum, from three-quarters to four-fifths of the entire 
space occupied by the set gypsum is water. In the one case one 
hundred parts contain twenty parts of water, of which ten 
will go out at 21 2 \ In the other case one hundred parts of 
gypsum are combined with and enclose one hundred j^arts 
of water, of which ninety parts will go out at 21 2 \ At 
300^ the former will give up fifteen parts and the latter nine- 
ty-five. 

COMPOSITION YIELDING VAPOE ONLY AT 212^ AND ABOVE. 

The question of using a composition which should give up 
vapor at a temperature above 212° only, was tested in the 
use of a mixture of sulphate of ammonia and common salt 



12 

diluted with powdered coke, which on the application of 
heat, yielded sal ammoniac. Experiments were also made 
with a mixture of ammonia-alum and common salt, diluted 
like the above with coke. This yielded water in addition to 
sal ammoniac. Clay and powdered brick were substituted 
for coke. They gave results inferior to all except the potash- 
alum. 

In addition to these Laboratory experiments, a series ,was 
undertaken on a scale of such magnitude as to render the 
results of more direct practical value. As the object was to 
determine the relative excellence of different kinds of safes 
in which all the circumstances of exposure were the same, it 
was conducted with great attention to details, and was,9on 
many accounts, the most important ever made of which any 
record has been preserved. 

Through the cooperation of Mr. Anson Hardy, a safe 
manufacturer, of Boston, and the Messrs. Hinckley, Williams 
& Co., iron founders, of Boston, the necessary facilities were 
provided. 

EXPERIMENTS IN KEVERBEHATOIIY FUENACES. 

Five wrought iron safes were constructed, each of one 
cubic foot capacity. For each a small wooden box four inches 
in the clear, and three-quarters of an inch in thickness, Avas 
prepared to represent the inside case. "When in place, there 
was a space for composition of three inches thickness on 
every side of the box. In each wooden box was placed a 
piece of parchment, some white writing paper, cotton batting, 
a piece of sealing wax, a self-registering thermometer ranging 
to 600°, and a series of small thermometers bursting at 
given temperatures. 



13 



No. 1 contained Sulphate of Ammonia, 


15.5 lbs. 


Common Salt, 


15.5 " 


Powdered Coke, 


24 '' 


Wooden box. 


2 " 


Iron shell, 


27 " 


Total, 


84 lbs. 


No. 2 contained Potash-alum, 


26 lbs. 


Pipe clay. 


26 " 


Brick, 


28| " 


Dry cement to fill. 


1 " 


Wooden box. 


2 " 


Iron shell, 


28| " 




112Ubs. 


No. 3 contains Ammonia-alum, 


26 J lbs. 


Common salt. 


13^ '' 


Coke, 


16 " 


Wooden box. 


2 " 


Iron sheU, 


29i " 


r 


87J lbs. 


No 4 contained Cement, 


60 lbs. 


Water, 


19| " 


Soapstone front, 


9 " 


Wooden box, 


2 " 


Iron shell, 


30 " 




120| lbs 


No. 5 contained Plaster of Paris, 


50 lbs. 


Water, 


21 " 


Dry cement to fill. 


9 " 


Wooden box. 


2 " 


Iron shell, 


28 " 



110 lbs. 

These safes were carefully introduced into a reverberatory 
2 



furnace from which a discharge of twenty thousand pounds 
of molten iron had just taken place, and when the walls were 
nearly at the temperature of melted iron. The safes were 
placed on the bottom of the furnace, the door closed, and 
after adjusting the draft so as to permit the furnace to cool 
slowly down in the usual way, the safes were left from five 
o'clock in the afternoon till ten the next morning. 

RESULTS OF THE EXPERIMENT. 

On taking the safes from the furnace they were first weighed. 
No. 1 had lost 8i lbs. 
No. 2^' " " 15| " 
No. 3 " " 16| "t 
No. 4 " " 13 " 
No. 5 " " 16 " 

The temperature of No. 1 had been above 600 \ The 
paper, cotton batting and box were charred ; the parchment 
and sealing wax were destroyed. 

The temperature of Number 2 had been as high as 580"'. 
The paper, cotton and box were charred. The parchment 
and sealing wax were destroyed. 

The temperature of No. 3 had been 350\ Contents were 
much less injured than those of No. 1 and No. 2, but were 
still greatly discolored. The box was partially charred. 

The temperature of No. 4 was 287'. The paper and 
cotton were discolored. The box thoroughly dried and 
shrunken somewhat, but not charred. The parchment was 
shrivelled and the sealing wax melted. 

* This is the common Alum safe, except that one-third of alum was 
employed instead of one-quarter. 

t One pound of this and of each of the preceding two", is due to 
the charring of the wooden box. 



15 

The temperature of No. 5 had been 212°. The parch- 
ment was somewhat shrivelled and sealing wax melted, but 
the paper, cotton batting and box were uninjured. 

In the safes filled with potash-alum, clay and brick, — witl 
ammonia-alum, salt and coke, — and with sulphate of ammo- 
nia, salt and coke, a coarse porous wall around the interior 
wooden case was preserved after the volatile matters had 
been driven out. 

In the cement safe the cement retained about one-thii-d of 
its water and the form perfectly. 

In the gypsum and water safe the plaster retained its form. 
It had parted with about four-fifths of its water. (Strictly J-f .) 

From the foregoing, it is evident that in keeping the tem- 
perature down a given time 

7| lbs. of sal ammoniac are inferior to 

14| " " water from potash-alum; and these inferior to 

15| " " water and sal-ammoniac, from ammonia-alum 
sand salt ; and these inferior to 

13 " " water from the cement safe ; and these inferior to 

16 " " water from the plaster and water safe. 

In the gypsum and water safe, 5 pounds of water were 
fixed in the setting, and 16 pounds were held by capillary 
attraction. These 16 were driven out at 212 \ There 
remained five in combination at the close of the experiment 
to be driven out at the same temperature. 

In the cement safe, 6 pounds were fixed in the setting, and 
ISf pounds were held by capillary attraction. Of these 13|, 
13 were driven out at 21 2~. There remained but | of a 
pound to be driven out at 212^. 

In the Alum safe there were but 8 lbs. expelled at 212^. 

In summary — 



16 

The gypsum and water safe lost 16 lbs. at 212"^. 
" cement " " " " 13 " " " 
" alum " " 8^' " " " 

The water remaining to be expelled, at 212°, from the gyp- 
sum and water safe, was 5 lbs. 

From the cement safe, was f lb. 
" " alum " " 0. 

Not only was there no water to be driven out at 212\ but 
G| lbs. had been driven out at much higher temperatures, 
the last at 580°. 

A cement safe, as ordinai'ily made, set and dried, of these 
dimensions, Contains a little more than half a pound of water 
to be driven out at 212 \ In a plaster safe, set and dried, 
there would have been but 5 lbs. to be driven out at 212^. 
In an ordinary alum safe, there would have been less than 
eight; while in the gypsum and water safe, as here prepared, 
there were 21 lbs., which, by the process already described, 
might have been increased to 50 lbs. 

The potash-alum safe lost altogether within 1^ lbs. as much 
water as the plaster and water safe, but nearly one-half went 
out at temperatures from 212^ to 580^, a range destructive to 
books and papers. The ammonia-alum and salt safe lost 
about 20 per cent, more of water and sal ammoniac than the 
cement safe of water alone, and yet did aiot afford the same 
degree of protection, for the cement safe was heated only to 
287^t, while the ammonia safe was heated to 350 \ 

*A part of this loss was evidently due to the moisture in the clay. 

fThis elevated temperature, while there was still water in the 
c ement, is manifestly due to the conducting power of the soap stone 
upon which the wooden box rested. 



17 



EXPERIMENT IN FURNACE AT AVHITE HEAT. 

Another experiment was undertaken with four safes of the 
capacity of one cubic foot each. Each contained a wooden 
box, enclosing a series of thermometers constructed to burst 
at given temperatures. 

No. 1 contained Cement, 64 lbs. 

Water, 3| " 

This is cement containing the quantity of water which 
remains after the filling is set and dried. 

No. 2 contained Plaster, 62j lbs. 

Water, 12 " 

This is a plaster of paris safe, containing twenty-five per 
cent, more than the quantity of water due to plaster set and 
dried. 

No. 3 contained Alum, 33 lbs. 

Pipe Clay, 33 '* 

Brick, 19J " 
This safe, with a smaller proportion of alum, is in extensive 
use in this country. 

No. 4 contained Plaster, 28 lbs. 

Gelatine,* U " 

Water, 43 " 

These safes were placed in the same reverberatory furnace 
in which the preceding experiment was conducted. There 
was this difference between the experiments : The first was 

* I employ the term Gelatine as expressing in a single word the sub- 
stance obtained by the action of boUing water from gelatinizalle sub- 
stances, like sea- weed, of the variety known as Iceland moss, or pota- 
to 3 starch, or animal membranes, or from other similar vegetable and 
animal substances. 



18 



conducted with a constantly falling temperature. This with 
a temperature carried from freezing up to a white heat, and 
there maintained for thirty minutes ; and then permitted to 
cool down. 

At the end of the first half hour, Nos. 1 and 2, which 
were least exposed, were red hot ; No. 3 was at low red, and 
No. 4 was dark. 

At forty minutes the condition was the same. 

At forty-two minutes, pronounced melting heat, by the* 
workmen, Nos. 1, 2, and 3, were red, but 4 still dark equally 

At fifty minutes. No. 4 became low red, and No. 3 was 
burned through and melted away at points nearest the fire. 

At 60 minutes, No. 3 was at a white heat, and No. 4 was 
red. 

This w^hite heat was maintained for thirty minutes, when 
the furnace was opened and cooled down sufficiently to exam- 
ine the condition of the safes. 

No. 4 was burned so as to crack a little on one side, but 
was not melted in any part. 

No. 3 was melted away from the top, front, and two sides. 
The side farthest from the fire, and bottom, were alone whole. 

No. 2 was scarcely less injured. The melting did not, 
however, extend so far down the sides. 

No. 1 , which was further from the fire and sheltered by the 
other safes, was burned but not melted. 

The fire was again raised to the melting point, the furnace 
closed, and the safes left in this heated chamber, slowly cool- 
ing down, from 5 o'clock in the afternoon till 10 o'clock the 
next morning. 

On opening the furndlte, the appearances of the safes had not 
apparently changed since the examination at the close of the 



19 



first experiment. The wooden boxes in Nos. 1, 2, and 3, 
had been destroyed. The temperature in No. 2 had been 
above 600^, and in Nos. 1 and 3, above 300^, but not to 
600'', though probably not far below. 

The wooden box in No. 4, was as fresh as when put in. 
The thermometer bursting at 150^ was destroyed, but that 
bursting at 212^, was sound. The heat had not attained to 
that of boiling water. It will be borne in mind that No. 1 is 
the ordinary cement saf:, No. 2 is the ordinary plaster of 
paris safe. No 3. is the alum safe, and No. 4 the new safe. 
The first three were destroyed, while the temperature in No. 
4 was, at the utmost, entirely within the range of safety to 
the books and papers. 

CONCLUSIONS IN TIEW OF THE FOKEGOING EXPEKIMENTS. 

1st. It is evident that the protection against fire is mainly 
joroportioned to the quantity of water the safe can give up to he 
carried away as steam, and not to the non-conducting quality 
of its filling. 

2d. It is evident, further, that the protection against fire is 
not simply as the quantity of water that may be present in 
the composition for filling, but as the quantity of water that 
may be parted with unrestrained hy chemical affinity, or water 
AS SUCH. The more powerful the chemical affinity resisting the 
escape of vapor the more elevated must be the temperature 
at which it will leave, while the capacity of the escaping 
vapor to render heat latent or to absorb and carry it away will 
remain unchanged. The same quantity of water in combi- 
nation in alum is not so serviceable in keeping down the 
temperature as when free. 

3d. It is evident, further, that while the water in its un- 



20 

combined or natural state must constitute a large part of the fil- 
ling of a safe in order to make its protection against fire, in 
the highest degree, available, this water must be held in solid 
form so as to give strength to the safe ; and the safe must be 
so constructed as to prevent the water from passing off by 
leakage, or as vapor to the injury of the books and papers, 
or to the lessening of the fire proof qualities of the safe ; and 
yet be so constructed as to allow, on the application of high 
heat, the most free escape of vapor, from those points to 
which the heat is applied, without endangering the strength 
of the safe, or driving the vapor into the interior chamber of 
the safe ; and withal so arranged as to permit freezing, with- 
out injury to the safe or its contents. 

In a safe made in the light of the foregoing experiments, 
from 70 to 80 per cent, of the space appropriated to filling, 
was occupied by water, and yet was exposed for a da^' and 
two nights to a temperature of zero without injury. 

On exposure to fire the water is resolved into vapor first 
at the outer surface of the filling, and leaves the best non- 
conductor according to the results of foregoing experiments, 
(see pages 8 and 9,) between the water which remains and 
the heated metal of the exterior shell. At length, when all 
the water has been driven out as vapor, there remains the 
non-conductor of the whole thickness of the filling, to protect 
as long as it may, the contents of the case. 



21 



SUMMARY. 

The demands for an improved safe have been met as 
follows : 

1 . By securely providing for evaporation by exposure to 
fire, with a given weight of filling, from two to ten times as 
much available water as is furnished by any safe in use, and 
gaining thereby a corresponding increase of protection 
against fire. 

2. By securing a better non-conductor, after the water 
has been driven from the filling, than any hitherto devised. 

3. By so constructing the safe as absolutely to prevent any 
escape of water or vapor from the filling to the interior 
chamber of the safe, thereby securing the books and papers 
against dampness. 

4. By so constructing the safe as to provide for the ex- 
pansion of the water consequent on freezing, without opening 
the joints or seams ; thus while making it possible greatly to 
increase the quantity of water the safe will contain, at the same 
time securing the safe, primarily against injury from frost, and 
secondarily from the exhalation of moisture through the open- 
ings produced by the frost, causing injury to the contents of 
the safe. 

5. The great excess of water or of protecting power 
against fire, in the filling employed, allows a reduction of the 
thickness of the filling. With a reduction of the thickness, 
there is, Avith a given exterior, a larger interior space for the 
contents of the safe. With this reduction in thickness there 
is also corresponding reduction in the weight of the safe, and 
if advantage be not taken of the increased space for the case, 
it may be taken in the diminished size of the shell ; and 
this will be accompanied by reduction in the cost of the safe. 



Safes made in accordance with the results of this research, 
may be seen at the office of the Tremont Safe and Machine 
Co , No. 32, School St, Boston. 



LIBRARY OF CONGRESS 




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LIBRARY OF CONGRESS 

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